The present invention relates to a method for inspecting printed circuit boards with through-holes. In the manufacture of conventional printed circuit boards with through-holes, after the through-holes are bored in the required positions, it is normal practice to pack conductive paste into the through-holes using a silk-screen printing method. Then, the packed conductive paste in each through-hole is visually inspected and current and voltage are measured between the top and bottom ends of the through-hole using the two-probe method on each printed circuit board or on circuit boards randomly selected from each lot.
In the above manufacturing process, it is difficult to use screen printing to spread conductive paste uniformly among all the through-holes of a printed circuit board or even in one printed circuit board, and the problem of incomplete packing thus arises. Unfortunately, the above-mentioned inspection and measurements are not always dependable and no other effective means for testing the packed conductive paste for electrical properties exists, thereby resulting in incomplete inspections. Therefore, an adequate testing means is desirable for conductive paste packed into through-holes on a printed circuit board.